i was going to put an intake on my 300ex, its bored .20 over, will this harm it.

 

no,
what do you mean an intake?

dude, put a uni filter on it, open the airbox lid, or drill a few holes in it, or get uni circle filter drop ins (to fill the holes)
or a LOW boy valve, or a outerwearz airbox lid, its like a mesh water proof lid that lets in tons of extra air..

you can than put a 350x air intake tube/boot in place or yours, it flows a bit more. you

should than jet your carb, and why not throw a full header and exhaust on there ,it will be a monster..

after that you should put a 14 tooth front sprocket to fill out your gears with your new found power

 

The 300 has a pathetic stock header. I put an FMF high flow header on and a PowerCore4 muffler, opened up the airbox, and a UNI air filter...and of course a rejet!